Zoom lens system

Claim 2

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refraction power that moves along the optical axis for zooming, a third lens group having negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power that is situated closer to the object than the aperture and a second sub-group having a positive refractive power that is situated closer to the image than the aperture and wherein the first sub-group is composed of at least two positive lens elements and at least one negative lens element.

Claim 3

A zoom lens system according to claim 1 wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element.

Claim 4

A zoom lens system according to claim 1, wherein said first lens group comprises a cemented lens of a negative meniscus lens element having a convex surface directed toward the object and a positive lens element, and a positive meniscus lens element having a convex surface directed toward the object; said second lens group comprises a negative lens element having a concave surface of a strong curvature directed toward the image, a biconcave lens element, and a positive lens element; and said third lens group comprises a single negative lens element.

Claim 5

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refraction power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power that is situated closer to the object than the aperture and a second sub-group having a positive refractive power that is situated closer to the image than the aperture and wherein said fourth lens group further satisfies the following conditions: ##EQU5## where f W is the focal length of the overall system at the wide-angle end, f Iv is the focal length of the fourth lens group f 1va is the focal length of the first sub-group, d IVI-A is the distance from the first surface of first sub-group to the aperture, and HHIV a is the distance between the principal points in the first sub-group of the fourth lens group.

Claim 6

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refraction power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power that is situated closer to the object than the aperture and a second sub-group having a positive refractive power that is situated closer to the image than the aperture and wherein said fourth lens group further satisfies the following conditions: ##EQU5## where f W is the focal length of the overall system at the wide-angle end, f Iv is the focal length of the fourth lens group f 1va is the focal length of the first sub-group, d IVI-A is the distance from the first surface of first sub-group to the aperture, and HHIV a is the distance between the principal points in the first sub-group of the fourth lens group.

Claim 7

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refraction power that moves along the optical axis for zooming, a third lens group having a negative refractive power than moves along the optical axis for compensating for the imaging plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power that is situated closer to the object than the aperture and a second sub-group having a positive refractive power that is situated closer to the image than the aperture, wherein the first sub-group comprises, in order from the object side, a positive lens element having a convex surface of a strong curvature directed toward the image, a positive lens element having a convex surface of a strong curvature directed toward the object, and a negative lens element having a concave surface of a strong curvature directed toward the object.

Claim 8

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refraction power that moves along the optical axis for zooming, a third lens group having a negative refractive power than moves along the optical axis for compensating for the imaging plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power that is situated closer to the object than the aperture and a second sub-group having a positive refractive power that is situated closer to the image than the aperture, wherein the first sub-group comprises, in order from the object side, a positive lens element having a convex surface of a strong curvature directed toward the image, a positive lens element having a convex surface of a strong curvature directed toward the object, and a negative lens element having a concave surface of a strong curvature directed toward the object.

Claim 9

A zoom lens system according to claim 5, wherein said first sub-group satisfies the following condition: ##EQU6## is the power of the divergent surface on the object side of the negative lens element in the first sub-group, n IVaN is the refractive index at the d-line of the negative lens element in the first sub-group, and r IVaN is the radius of curvature of the surface on the object side of the negative lens element in the first sub-group.

Claim 10

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refraction power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power that is situated closer to the object than the aperture and a second sub-group having a positive refractive power that is situated closer to the image than the aperture, wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element, wherein said second lens sub-group satisfies the following conditions: ##EQU7## is the power of the divergent surface on the image side of the negative lens element in the second sub-group, n IVbN is the refractive index at the d-line of the negative lens element is the second sub-group, r IVbN is the radius of curvature of the surface on the image side of the negative lens element in the second sub-group, and l IVa-IVb is the distance from the divergent surface of the first sub-group to the divergent surface of the second sub-group.

Claim 11

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refraction power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power that is situated closer to the object than the aperture and a second sub-group having a positive refractive power that is situated closer to the image than the aperture, wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element, wherein said second lens sub-group satisfies the following conditions: ##EQU7## is the power of the divergent surface on the image side of the negative lens element in the second sub-group, n IVbN is the refractive index at the d-line of the negative lens element is the second sub-group, r IVbN is the radius of curvature of the surface on the image side of the negative lens element in the second sub-group, and l IVa-IVb is the distance from the divergent surface of the first sub-group to the divergent surface of the second sub-group.

Claim 12

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power, and wherein the first sub-group comprises, in order from the object side, a positive lens element having a convex surface of a strong curvature directed toward the image, a positive lens element having a convex surface of a strong curvature directed toward the object, and a negative lens element having a concave surface of a strong curvature directed toward the object, and wherein said first sub-group satisfies the following condition: ##EQU8## is the power of the divergent surface of the object side of the negative lens element in the first sub-group, n IVaN is the refractive index at the d-line of the negative lens element in the first sub-group, and r IVaN is the radius of curvature of the surface on the object side of the negative lens element in the first sub-group.

Claim 13

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power, and wherein the first sub-group comprises, in order from the object side, a positive lens element having a convex surface of a strong curvature directed toward the image, a positive lens element having a convex surface of a strong curvature directed toward the object, and a negative lens element having a concave surface of a strong curvature directed toward the object, and wherein said first sub-group satisfies the following condition: ##EQU8## is the power of the divergent surface of the object side of the negative lens element in the first sub-group, n IVaN is the refractive index at the d-line of the negative lens element in the first sub-group, and r IVaN is the radius of curvature of the surface on the object side of the negative lens element in the first sub-group.

Claim 14

A zoom lens system according to claim 8 wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element.

Claim 15

A zoom lens system according to claim 8, wherein said first lens group comprises a cemented lens of a negative meniscus lens element having a convex surface directed toward the object and a positive lens element, and a positive meniscus lens element having a convex surface directed toward the object; said second lens group comprises a negative lens element having a concave surface of a strong curvature directed toward the image, a biconcave lens element, and a positive lens element; and said third lens group comprises a signal negative lens element.

Claim 16

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power and wherein said fourth lens group further satisfies the following conditions: ##EQU9## where f W is the focal length of the overall system at the wide-angel end, f IV is the focal length of the fourth lens group, and f IVa is the focal length of the first sub group.

Claim 17

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power and wherein said fourth lens group further satisfies the following conditions: ##EQU9## where f W is the focal length of the overall system at the wide-angel end, f IV is the focal length of the fourth lens group, and f IVa is the focal length of the first sub group.

Claim 18

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power, wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element, and wherein said first lens sub-group satisfies the following conditions: ##EQU10## is the power of the divergent surface on the image side of the negative lens element in the second sub-group, n IVbN is the refractive index at the d-line of the negative lens element in the second sub-group, and r IVbN is the radius of curvature of the surface on the image side of the negative lens element in the second sub-group.

Claim 19

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power, wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element, and wherein said first lens sub-group satisfies the following conditions: ##EQU10## is the power of the divergent surface on the image side of the negative lens element in the second sub-group, n IVbN is the refractive index at the d-line of the negative lens element in the second sub-group, and r IVbN is the radius of curvature of the surface on the image side of the negative lens element in the second sub-group.

Claim 20

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power, wherein the second sub-group comprises, positive refractive power, wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element, and wherein said first lens sub-group satisfies the following condition: ##EQU11## where l Iva-IVb is the distance from the divergent surface of the first sub-group to the divergent surface of the second sub-group.

Claim 21

In a zoom lens system which comprises, in order from the object side, a first lens group having a positive refractive power that moves along the optical axis for focusing, a second lens group having a negative refractive power that moves along the optical axis for zooming, a third lens group having a negative refractive power that moves along the optical axis for compensating for the image plane that varies upon zooming, and a fixed, imaging fourth lens group having a positive refractive power, the improvement wherein the fourth lens group has a variable aperture for variable controlling the amount of light that passes therethrough and comprises a first sub-group having a positive refractive power and a second sub-group having a positive refractive power, wherein the second sub-group comprises, positive refractive power, wherein the second sub-group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object and a biconvex positive lens element, and wherein said first lens sub-group satisfies the following condition: ##EQU11## where l Iva-IVb is the distance from the divergent surface of the first sub-group to the divergent surface of the second sub-group.